GDG DevFest 2015 - Reactive approach for slowpokes

REACTIVE
APPROACH
FOR SLOWPOKES
BY SERGEY TARASEVICH

• “раздуплить”
• “я бы тоже хотел думать мозгом”
• “я понимаю, шо я так сходу лиспом в
голову”
• “оно производит изменения в мозгу,
которые делают программиста лучше”
• “чик-чик и в продакшн”
WHAT’S LEARNED

REACTIVE IS …
• Functional
• Avoid intricate stateful programs, using clean input/output functions over
observable streams.
• Less is more
• ReactiveX's operators often reduce what was once an elaborate challenge into a
few lines of code.
• Async error handling
• Traditional try/catch is powerless for errors in asynchronous computations, but
ReactiveX is equiped with proper mechanisms for handling errors.
• Concurrency made easy
• Observables and Schedulers in ReactiveX allow the programmer to abstract
away low-level threading, synchronization, and concurrency issues.

ONE DOES NOT SIMPLY
BECOME REACTIVE

• New approach
• New thinking
• New data flow
• New error handling
• New language?
WHAT’S NEW?

RXJAVA + JAVA 7
Удобно пи ец

Observable
.range(1, 4)
.delay(new Func1<Integer, Observable<Integer>>() {
@Override
public Observable<Integer> call(final Integer integer) {
return MathObservable
.sumInteger(Observable.range(1, integer))
.flatMap(new Func1<Integer, Observable<Integer>>() {
@Override
public Observable<Integer> call(Integer targetSecondDelay) {
return Observable
.just(integer)
.delay(targetSecondDelay, TimeUnit.SECONDS);
}
});
}
})
.doOnSubscribe(new Action0() {
@Override
public void call() {
_log(“…”);
}
})
.subscribe(new Observer<Integer>() {
@Override
public void onCompleted() {
Timber.d("onCompleted");
IN JAVA

RXJAVA + JAVA 8
Java 8 on Android

RXJAVA + JAVA 8λ + RETROLAMBDA

Observable
.range(1, 4)
.delay { integer ->
MathObservable
.sumInteger(Observable.range(1, integer))
.flatMap { targetSecondDelay ->
Observable
.just(integer)
.delay(targetSecondDelay, TimeUnit.SECONDS)
}
}
.doOnSubscribe {
Timber.d(“…”)
}
.subscribe(
{ integer -> Timber.d(“…”) },
{ error -> Timber.d(error, "arrrr. Error") },
{ Timber.d("onCompleted") }
)
IN KOTLIN

TERMINS
• Observable / Single
• lift(Operator)
• subscribeOn(Scheduler) / observeOn(Scheduler)
• subscribe(Observer)
• Observer
• onNext()
• onError()
• onComplete()
• Subject = Observable + Observer
• Operators (map, flatMap, merge, delay, …)
• Schedulers

OBSERVABLE
Single Multiple
Sync T getData() Iterable<T> getData()
Async Future<T> getData() Observable<T> getData()

OBSERVABLE
Single Multiple
Async Future<T> getData() Observable<T> getData()
© Ben Christensen (Netflix)

OBSERVABLE
Single Multiple
Async
Future<T> getData()
Single<T> getData()
Observable<T> getData()

OBSERVABLE
Iterable Observable
T next() onNext(T)
throws Exception onError(Exception)
!hasNext() onComplete()

OBSERVABLE
observable
.map { … }
.subscribe(
{ data -> log(“onNext()”) },
{ error -> log(“onError()”) },
{ log(“onComplete”) }
)

RXMARBLES.COM
• observable.first()
• observable.filter { x -> x > 10 }
• observable.delay(10, SECONDS)
• observable.mergeWith(observable2)
• observable.debounce(1, SECONDS)
• observable.skipUntil(observable2)

OBSERVER
observable
.map { … }
.filter { … }
.subscribe(
)
}Observer

OBSERVER
observable [“хочу сапоги”, “хочу шубу”, “хочу телефон”, …]
.map { … } [“сапоги” -> $200], [“шуба” -> $1000], …
.filter { … } [ ценник < $500 ]
.subscribe(
{ data -> log(“onNext()”) }, Окей, записал
)

OBSERVER
observable [“хочу парня нормального”]
.map { … } [#ERROR]
.filter { … } [#ERROR]
.subscribe(
{ error -> log(“onError()”) }, o_O
)

OBSERVER
observable [Ой, все!]
.map { … } [Ой, все!]
.filter { … } [Ой, все!]
.subscribe(
{ log(“onComplete”) } Ой, все!
)

SUBJECT
Subject = Observable + Observer

SUBJECT
observable
.map { … }
.filter { … }
.subscribe(
)

SUBJECT
observable subject
.map { … }
.filter { … }
.subscribe(
)

SUBJECT
observable
.map { … }
.filter { … }
.subscribe(subject)
)

SUBJECT
• PublishSubject
• BehaviorSubject
• ReplaySubject
• AsyncSubject

SUBJECT
• PublishSubject - for Junior
• BehaviorSubject - for Middle
• ReplaySubject - for Senior
• AsyncSubject - for PM

SCHEDULERS
observable
.subscribeOn(…)
.observeOn(…)
.subscribe {
…
}

SCHEDULERS
observable
…
.observeOn(AndroidSchedulers.mainThread())
.subscribe {
textView.setText(…)
} wow
so mainthreadish

NETWORK LAYER
RestFacade
——————————————————————————————————————————————————
void getUser(Params params,
DataListener<User> listener)
void pullUserNotifications(Params params,
DataListener<Notification> listener)
void saveProfile(UserProfile profile)

MODEL LAYER
UserService(RestFacade)
——————————————————————————————————————————————————
void getProfile(UserProfileListener listener) { … }
void addUserNotificationListener(
NotificationListener listener) { … }
void startListenNotifications() { … }
void stopListenNotifications() { … }

VIEW (IVIEW) LAYER
IUserView
——————————————————————————————————————————————————
void setName(String name)
void setOnSaveProfileListener(Listener listener)
——————————————————————————————————————————————————
INotificationsView
——————————————————————————————————————————————————
void setNotifications(List<Notification> notifications)
void setOnNotificationClickListener(
Listener<Notification> listener)
——————————————————————————————————————————————————

PRESENTER LAYER
UserProfilePresenter(UserService, IView)
——————————————————————————————————————————————————
private UserProfile profile;
private List<Notification> notifications;
void init() {
userService.addUserNotificationListener(this)
view.setOnSaveProfileListener(this)
userService.getUserProfile(this)
userService.startListenNotifications()
}

PRESENTER LAYER
——————————————————————————————————————————————————
@Override
void onUserProfileReceived(UserProfile profile) {
this.profile = profile
view.setName(profile.name + “ “ profile.lastName)
}
@Override
void onNotificationReceived(Notification notif) {
this.notifications.add(notif)
view.setNotifications(this.notifications)
}
@Override
void onSaveProfile() {
userService.saveProfile(…)
}

LAYERS 1.0
L
L
L
C
C
C
L - listener
C - call

LAYERS 2.0
L - listener
C - call
O - observable
O
L
L
C(o)
C
C

LAYERS 3.0
L - listener
C - call
O - observable
O
O
LC
C(o)
C{}

LAYERS 4.0
L - listener
C - call
O - observable
O
O
O
C{}
C
C(o)

NOT SURE
IF RETROFIT IS ALREADY REACTIVE

NETWORK LAYER 1.0
RestFacade
——————————————————————————————————————————————————

NETWORK LAYER 2.0
RestFacade
——————————————————————————————————————————————————
Observable<User> getUser(Params params)
Observable<Notification> pullUserNotifications(
Params params)
Observable<Void> saveProfile(UserProfile profile)

MODEL LAYER 1.0
——————————————————————————————————————————————————

MODEL LAYER 2.0
——————————————————————————————————————————————————
Observable<UserProfile> getProfile() { … }
Observable<Notification> getNotifications() { … }

VIEW (IVIEW) LAYER 1.0
IUserView
——————————————————————————————————————————————————
——————————————————————————————————————————————————
INotificationsView
——————————————————————————————————————————————————
——————————————————————————————————————————————————

VIEW (IVIEW) LAYER 2.0
IUserView
——————————————————————————————————————————————————
Observable<Void> saveProfileClicks()
——————————————————————————————————————————————————
INotificationsView
——————————————————————————————————————————————————
Observable<Notification> notificationClicks()
——————————————————————————————————————————————————

PRESENTER LAYER 1.0
——————————————————————————————————————————————————
private UserProfile profile;
private List<Notification> notifications;
void init() {
userService.addUserNotificationListener(this)
view.setOnSaveProfileListener(this)
userService.getUserProfile(this)
userService.startListenNotifications()
}

PRESENTER LAYER 1.0
——————————————————————————————————————————————————
@Override
void onUserProfileReceived(UserProfile profile) {
this.profile = profile
view.setName(profile.name + “ “ + profile.lastName)
}
@Override
void onNotificationReceived(Notification notif) {
this.notifications.add(notif)
view.setNotifications(this.notifications)
}
@Override
void onSaveProfile() { userService.saveProfile(…) }

PRESENTER LAYER 2.0
——————————————————————————————————————————————————
void init() {
userService.getUserProfile()
.map { profile -> formatName(profile) }
.subscribe { name ->
view.setName(name)
}
userService.pullNotifications()
.subscribe { notifications ->
view.setNotifications(notifications)
}
…
}

PRESENTER LAYER 2.0
——————————————————————————————————————————————————
void init() {
…
view.saveProfileClicks()
.withLatestFrom(currentProfileStream, …)
.flatMap { profile ->
userService.saveProfile(profile)
}
.subscribe(
{ success -> …},
{ error -> … }
{ … }
)
}

YOU SUBSCRIBE TO OBSERVABLE
BUT FIRE CALLBACK IN ONNEXT()

BE ATTENTIVE
Observable<Void> saveProfile(UserProfile profile)
• userService.saveProfile(userProfile)
Do nothing!
• userService.saveProfile(userProfile).subscribe()
Do the thing!

BEHAVIOUR SUBJECT
Observable<Data> stream =
new BehaviorSubject(data)
…
stream.subscribe { data ->
… // first onNext() event is on the same thread
}

CONNECTABLE STREAM
ConnectableObservable statuses()
——————————————————————————————————————————————————
…
Subscription s = statuses().connect()
…
statuses().subscribe(…)
…
s.unsibscribe()
statuses().connect()
…

CONNECTABLE STREAM
ConnectableObservable statuses()
——————————————————————————————————————————————————
…
Subscription s = statuses().connect()
…
statuses().subscribe(…) // Where is my data?
…
s.unsibscribe()
statuses().connect()
…

• Easy to understand?
• Easy to use?
• Huge error stacktraces?
• GC works hard?
• Low performance?
FAQ

• RxJava is cool (with Kotlin)
• You can become reactive step by step
• It makes you happier
SO…

LINKS
• http://reactivex.io/
• http://rxmarbles.com/
• https://github.com/ReactiveX/RxJava
• https://www.youtube.com/watch?
v=SyWFvn0I6m8
• https://speakerdeck.com/benjchristensen/
functional-reactive-programming-in-the-netflix-
api-lambdajam-2013

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